An electrocardiogram (ECG) monitoring apparatus is a medical device that receives and processes ECG signals generated by a circulatory system of a person, e.g., the electrical impulses that trigger various phases of a heartbeat. The apparatus typically includes a plurality of patient-contact electrodes (“electrodes,” “skin-contact biopotential electrodes,” or “SCBEs”), each electrically connected via a wire to a voltage detector. The patient-contact electrodes make physical contact with the person being monitored, e.g., on the person's skin. The ECG electrodes and wires receive and relay ECG signals generated by the person to components of the ECG monitoring apparatus that process the ECG signals.
FIG. 1 is a partially-schematic view of a conventional ECG monitoring apparatus including six ECG patient contact wires 103 connected to respective patient-contact electrodes 101. (Any number of electrodes and wires can be used.) Electrodes 101 are configured to be attached to the skin of a person or other animal (e.g., a dog, cat, bird, or other pet), also referred to as a patient or subject (subject 38, shown in phantom for purposes of orientation throughout this disclosure). Electrodes 101 are shown attached to the left arm, right arm, left leg, and chest of subject 38. ECG unit 186 receives ECG signals generated by the patient (not shown) via ECG wires 103 and processes those signals. ECG unit 186 provides to a caregiver representation(s) of one or more electrode voltage(s) or voltage difference(s). The representation(s) can be, e.g., printouts on graph paper or continually-updated traces on a display screen of ECG unit 186. In carrying out an ECG examination, ECG electrodes 101 can be attached to points on the upper body (e.g., chest and arms) or lower body (e.g., legs) of the patient. Further details regarding the placement and orientation of the electrodes and workings of an ECG apparatus is known to those in the field, such as provided in U.S. Pat. No. 7,618,377B2, incorporated herein by reference.
Skin-contact electrodes based on measuring biopotentials (e.g., electrodes 101) are used in various medical examination apparatus, notably electrocardiograms (ECG or EKG) that measure heart activity. They are also used for electroencephalograms (EEG) that measure brain activity and electromyograms (EMG) that measure the electric potentials generated by skeletal muscles. In the course of examination, some ECG applications use 10 (ten) or more individual wires, each with a corresponding electrode. Moreover, the electrodes used are generally identical to reduce measurement variation and electrode measurement cost. As a result, wires can readily be attached to the wrong electrodes.
Furthermore, many electrodes are provided with an adhesive element that permits an operator to adhere the electrodes to the skin of subject 38. An operator can be, e.g., a medical professional or other caregiver, a subject himself or herself, or a member of the subject's family, e.g., the subject's spouse. Electrode adhesives can have a limited shelf life, after which they will no longer adequately adhere to the subject. An issue is that loose electrodes are not readily identified by the caregiver, creating significant delays and errors in the examination process, whether in the course of a scheduled medical examination in a medical facility or in situations in which an apparatus such as a Holter assembly is worn for longer periods of time.
GB 2418365 A describes skin contact electrodes used with test circuits. Two contact areas are electrically connected through skin contact gel and a conductive backing layer. Before the electrode is applied to a patient, and before the backing layer is removed in preparation for doing so, the impedance through the gel and backing layer between the two contact areas is determined. The condition of the gel is inferred from the determined impedance.
However, this scheme does not permit determining the quality of the connection between the electrode and the patient's skin. The gel condition is determined before the electrode is applied. Even if the gel is in operable condition, it can still fail to make effective electrical contact with the patient due to hair, sweat, skin oil, skin flakes, dirt, or other contaminants on the skin, misapplication of the electrode, or a defect in the electrode. There is, therefore, a continuing need for determining whether an electrode is effectively electrically coupled to a patient, whether initially or over the course of examination.
WO 2008/056309 attempts to address this need by injecting a signal into a patient through a reference electrode. The signal passes through the patient, and the ease of detection of the signal at an electrode other than the reference is an indication of the quality of the connection of that other electrode. However, this scheme requires a reference electrode, and it requires correlating readouts on a display screen attached to ECG unit 186 with the wires and electrodes on the patient's body, which can be an error-prone process. Wires are generally color-coded, but this does not help wholly- or partly-colorblind operators. U.S. Pat. No. 5,042,498 provides LEDs on electrode wires to indicate which wires are attached to poorly-connected electrodes, but these schemes require specialized wires and electrode adapters, and are not useful for circumstances such as home monitoring in which an ECG might be used by a patient instead of a doctor. U.S. Publication No. 20100081950 describes LEDs on the electrodes illuminated in a sequence, e.g., the path of a hand-drawn letter “e” across then around the chest, to visually highlight electrodes connected to the wrong wires. However, this scheme also requires specialized electrode wires and adapters. Moreover, this scheme requires special electrodes, so conventional electrodes cannot be used with a described ECG unit.
There is, therefore, a continuing need of more readily determining whether an electrode has reached the end of its useful life. There is also a need of a way of determining the quality of electrical contact between an electrode and the skin of the patient. There is a further need of doing so in a way that relieves an operator of the need to trace through a myriad of wires in order to identify the appropriate wire and electrode.